The overall goal of this project is to explore the regulatory mechanisms that control reproduction using a unique genetic model system, the hypogonadal, GnRH-deficient hpg mouse with replacement of GnRH by targeted gene therapy. The ultimate test for the ability of viral vector systems to successfully direct cell-specific, physiologically regulated GnRH expression and release is the full recovery of reproductive function in the hpg mice. One of the unique features of our viral transgene that is essential for the recreation of reproductive integrity is the use of the GnRH gene with its own cognate promoter. The use of the endogenous GnRH gene promoter may allow regulated, pulsatile GnRH production and release, and hence stimulate pituitary LH and FSH production and lead to activation of the reproductive axis and induction of fertility. Our preliminary studies in hpg females injected with HSV.GnRH.GFP amplicon demonstrate coordinated stimulation of pituitary LH and FSH secretion and ovarian and uterine growth. In the hpg male, we have demonstrated spermatogenesis after delivery of HSV.GnRH.GFP amplicon vector. We hypothesize that delivery and expression of the GnRH gene to hypothalamic neurons in adult female and male hpg mice will result in the full recapitulation of reproductive function. In the first aim, we propose to more fully characterize the extent of reproductive recovery achieved by GnRH gene therapy, including ovarian folliculogenesis and ovulation, spermatogenesis, sexual reproductive behavior and fertility. Successful activation of reproductive function in this model would also suggest that neuronal inputs to GnRH neurons remain intact in hpg mice, so that appropriate modulation of GnRH output can occur. In the second aim, the effects of GnRH rescue on the regulatory mechanisms that control reproduction will be explored, including peripheral modulators such as positive and negative feedback effects of sex steroids, and central modulators such as kisspeptin. The proposed studies provide a genetic model for selective and regulated gene replacement therapy, and thus may have important implications not only for reproductive disorders such as infertility, but also for applications of gene therapy in the neurosciences, for treatment of neurological and other disorders where normal gene regulation is critical.